Electric transformer



April 2, 1963 H, w. LORD 3,084,299

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United States Patent 3,084,299 ELECTRIC TRANSFORMER Harold W. Lord, Schenectady, N.Y., assignor to General Electric Company, a corporation of New York Filed May 1, 1358, Ser. No. 732,301 16 Claims. (Cl. 33670) My invention relates to a coil having primary and secondary windings.

Recent advances in high-powered electron discharge devices for pulsed operation in radar transmitters have increased the requirement for pulse operating voltages to 300 kilovolts, and future systems may require even higher voltage pulses. These high voltage pulses cannot be obtained from conventional pulse transformers because the individual insulation pads in them are subject to large portions of the output voltage, which at the high output voltages now being required, are often great enough to cause destruction of the insulation properties of these pads.

Accordingly, an object of the present invention is to provide an improved transformer capable of producing a large output voltage.

Another object is to provide a transformer in which only a small portion of the output voltage appears across any single insulation pad.

Arcs or sparks frequently occurring across electrodes in electron discharge devices of the pulse type, place a short circuit across the secondary windings of the voltage-supplying transformer, causing the terminal voltage to suddenly collapse from full-rated voltage to substantially zero voltage, which in turn, discharges the electrical energy stored in the distributed capacitance of the transformer. This produces a large current flow through some of the winding turns and thus a very large voltage across these turns, which is often great enough between some turns and layers of turns to produce ruptures in the insulation.

Therefore, another object is to provide a transformer in which the energy stored in the distributed capacitance does not produce a large transient voltage across any of the insulation of the transformer when suddenly discharged.

,Conventional ignition coils have additional insulation between the last layer or two of the secondary winding and fewer turns per layer in the last layer next to the secondary winding high voltage terminal to prevent interlayer and inter-turn insulation break-down due to the transient effects of the sparking across the spark plugs. Of course, it is more difficult and expensive to manufacture an ignition coil in which the winding layers of the secondary winding and the insulation between layers are not uniform as compared to ignition coils where they are uniform.

Thus, a further object of the present invention is to provide an ignition coil that may be uniformly wound and have uniformly thick insulation between winding layers.

In my copending application S.N. 732,348, filed May 1, 1958, now Patent No. 2,995,685, assigned to the assignee of the present invention, I disclose and claim an ignition system in which substantially all of the electrostatic energy stored in the ignition coil is available for firing spark plugs.

'Hence, another object of my invention is to provide an ignition coil from which substantially all of the electrostatic energy stored therein may be made available to an external circuit.

"These and other objects are achieved in one embodiment of my invention in which the primary and secondary windings'of a coil are wound to make the electrostatic energy storage per cubic volume of insulation substantially uniform over the coil. Shields around the windings produce capacitance coupling for discharging the distributed 3,084,299 Patented Apr. 2, 1963 capacitance energy of the coil without significant current flow through the winding turns.

The novel features that I believe are characteristic of my invention are set forth with particularity in the appended claims. My invention, itself, however, together with further objects and advantages thereof may best be understood by reference to the following description taken in connection with the accompanying drawings, in which:

FIG. 1 is a side view, partly in section, of a transformertype coil embodiment of my invention,

FIG. 2 is an enlarged partial section of the transformer of FIG. 1 included within the lines 2--2,

FIG. 3 illustrates the wiring designations for the winding turns of the embodiment of FIGS. 1 and 5,

FIG. 4 is a wiring diagram for the transformer of FIG. 1,

FIG. 5 is a partial cross-sectional view of another transformer-type coil embodiment of my invention, and

FIG. 6 is a partial, cross-sectional side view of an ignition coil embodiment of my invention.

In the several figures of the drawings, corresponding elements have been indicated by corresponding reference numerals to facilitate comparison. Referring specifically to FIG. 1, I have illustrated a transformer comprising a rectangular-shaped magnetic core 11 having legs 13 and 15 upon which are wound, respectively, a first winding set 17 and a second winding set 19. Each winding set includes portions of a primary winding and two secondary windings, which I will refer to as first and second secondary windings, separated by insulation pads 23 and enclosed in a tapered shield 25.

The turns of the various windings may be identified by the illustrations of FIG. 3 in which the primary turn designation is a circle containing cross-hatching at an angle of from the horizontal, the first secondary turn designation is a circle with cross-hatching at an angle of 30 from the horizontal, and the second secondary turn designation is a circle with cross-hatching at 60 from the horizontal.

From these designations it is seen that winding set 17 of FIG. 1 comprises a first layer 27, a fourth layer 33, and a sixth or outer winding layer 37 of turns of the second secondary winding, while a second layer 29 comprises turns of the primary winding and a third layer 31 and a fifth layer 35 comprise turns of the first sec ondary winding. In winding section 19 the first winding layer '39, a fourth Winding layer 44, and a sixth or outer layer 46 comprise turns of the first secondary Winding. A second winding layer 41 comprises turns of the primary Winding and a third winding layer 43 and a fifth winding layer 45 comprise turns of the second secondary winding. As is conventional, the number of winding layers depends only upon the desired increase in votalge. Specifically, with the same number of turns in each winding layer, the number of winding layers for each secondary winding is equal to the voltage increasing factor of the transformer, which is five for the illustrated transformer.

The winding layers are inter-connected by some leads 51, the heavy solid-line indicated ones of which connect the primary winding layers in parallel with subtractive polarity, the light solid-line indicated ones of which connect the first secondary winding layers in series additive, and the light dashed-line indicated ones of which connect the second secondary winding layers in series additive.

The winding layers have several significant features.- For example, all of the winding layers have the same" number of turns so that the same voltages are. induced into each, which, although not absolutely necessary, is preferred. winding layers, all of these winding layers must be Wound in the same manner, such that if they are all Also, for the shown connections betweenwound upon the same mandrel, each winding layer must be wound progressing in the same direction for a given direction of mandrel rotation. However, it is the voltage distribution between winding layers and not the manner of winding that is desired. Consequently, the winding layers may be wound differently and the connections between the winding layers changed from those shown so that the voltage distribution between winding layers is the same.

In each winding set 17' and 19, the winding layers from the third to the last are alternately taken from the two secondary windings with the last winding layer in one winding set being from a different secondary winding than the last winding layer in the other winding set. Furthermore, the primary winding is comprised of the second winding layer in both winding sets 17 and 19 to obtain closest coupling between the primary and secondary windings. With this arrangement the primary winding layers are closer to the secondary winding layers than they would be if the primary winding layers were in the first layers. Consequently, there is less flux leakage. However, as regards voltage distribution, the result is the same whether the primary winding comprise the first or second winding layers.

The shields 25, which are connected to the high voltage turns of the respective winding sets 17 and 19, are substantially identical. Each comprises a flat conductor 53 wound about a spiral-shaped insulator 55 formed with a progressively narrower width of insulation sheet so that it not only insulates the turns of conductor 53 but also produces a tapered form. Although the thickness of insulator 55 is illustrated in FIG. 1 as equal to that of the insulation pads 23, in most applications it will probably be much thinner, the determining factor being the dielectric constant. That is, the thickness and dielectric constant should be so related that the capacitance between the low voltage turn of the outer winding layers 37 and 46 of set 17 and 19, respectively, and therespective shields 25 is approximately equal to the capacitance between corresponding turns of the Winding layers. If insulator 55 is formed from the same material as insulator pads 23 then, obviously, the maximum thickness must beapproximately equal to the thickness of the insulation pads 23. This is illustrated in the partial cross-sectional view of FIG. 2.

The shields 25 need not be constructed from flat multiturn conductors but may be formed from any conductors that can be put in a tapered form. For example, they may be formed from a conductive film coated on a tapered insulator. In this case, a non-conducting line is required along the length of the shield to prevent it from acting as a shorted turn,

The input voltage is applied to the primary Winding between ground and a terminal,57. The increased output voltage is available between ground and either of two terminals 59 and 61 which are interconnected by a.

capacitor 6 3 having sufficient capacitance so that it presents' practically a short circuit across terminals 59 and 61 for the increased pulse output voltages.

The twin secondary windings provide a path for the heating current for the filament (not shown) of the electron discharge device to which the output voltage from the transformer is applied. The filament voltage is applied across the primary. winding of a transformer 65 having a secondary winding across which a capacitor 67' is connected. Capacitor 67, like capacitor 63, has a sufiiciently large capacitance to present a very low reactance to the pulses that are to be amplified by the voltage increasing transformer. However, for the low frequencies of the filament current, the reactances of capacitors 63 and 67 are high enough to present substantiallyopen circuits. The filament to be heated may be connected directly across terminals 59 and 61 or it may be transformer coupled to these terminals, depending upon, as is well known in the art, the nature of the 4 filament energy, the current carrying capacity of the twin secondary windings, and the voltage and current requirements of the filament. Thus, in some circuits there may be no filament transformers while in others one or maybe even two filament trans-formers may be required.

In FIG. 4, which is the winding arrangement for the coil of FIG. 1, the voltage to be increased is indicated for purposes of explanation, as 1,000 volts, which is also the voltage increase across all of the winding layers, since they all have the same number of turns. However, because the secondary winding layers, are connected in series additive, the voltages on these layers increase.

along the winding sets in a direction away from the core legs 13 and 15.

With the exception of the first two winding layers of each winding set 17 and 19, between which there is no induced voltage difference, there is only 1,000 volts between adjacent winding layers, which is the same voltage generated across the winding layers. Since the 1,000 volts input voltage was arbitrarily selected, it is generally true that the voltage across the insulation pads 23 is no greater than that across the winding layers. In other words, the voltages across insulation pads 23 are no greater than l/n times the output pulse voltage, wherein n is the voltage increasing factor'for the transformer, which is five for the illustrated number of secondary windings. Because of the small portion of the output voltage appearing across any of the insulation pads 23, a transformer may be designed with higher voltage gradicuts across these pads and yet still be conservatively designed. Also, there is a reduction in the voltage stress across a given insulation pad over that required for a comparable design in a conventional transformer.

The above statements relating to voltage distribution are valid only for non-transient voltages. In a consideration of transient voltages, which usually result from the short circuiting of terminals 59 and 61 to ground, shields 25 must be considered. If it were not for these shields, the delay line effect resulting from the distributed capacitance between winding layers and the inductance, primarily of the outer winding layers 37 and 46, would produce transient voltages across. the outer layers, immediately after the short circuiting of terminals 59 and 61 to ground, which are equal to 'the full secondary voltage Il'llIlUS the normal voltages across these outer layers. These large transient voltages, which would rupture the insulation between the outer, layer turns and also. the insulation pads between these and adjacentlayers, can

be considerably reduced if the distributed capacitance current flow through winding layers 37 and 46 is substantially eliminated. i

Shields 25 reduce the transient current flow through the winding layers 37 and. 46 by their capacitance coupllllg which provides a path. for this current that i orthogonal to the winding layers, or in other Words, is radial to the winding sets 17 and 119.. While-the use of shields 25 with a conventional transformer decreases this distributed capacitance current flow, their use with the transformer ofFIG. 1, substantially eliminates all of this current flow through the winding layers. This elimination is due to the uniform distribution of the energy in the distributed capacitance between winding layers; whichresults from the uniform distribution ofvolt-agesv between the winding layers. With uniform distribution of the energy there is substantially the same-currentfiow through each of the distributed capacitances and hence no tendency for this current to flow along the winding layers. Consequently, all of the potential voltages on the Winding layers, which aremaintained by the distributed capacitances, will have the same rate of fall to zero.

Actually, a small distributed capacitance current does' if optimum operation is desired, inner shields should be provided around legs 13 and 15, having surfaces parallel to the shields 25. However, as a practical matter, satisfactory results are obtained through use of shields 25 alone.

In FIG. 5 I have illustrated a transformer in which the voltage increasing factor is nine, although there are only five winding layers in each secondary winding. .This transformer is similar to that of FIG. 1 with the exception of the first two-winding layers in each winding set, which can be considered to be obtained by halving the number of turnsin the first two winding layers of each set of the transformer of FIG. 1 and combining them into a single winding layer. That is, the first winding layer of each set 17 and 19 of FIG. 5 is a bifilar winding layer comprising equal numbers of turns of the primary winding and one of the secondary windings. With this arrangement, the insulation pads 23 between the first and secondary winding layers of each set must withstand a greater voltage than that of the other insulation pads, but the increase in voltage is not very large. j

The statements aboverelating to the large voltages developed across the last or outer winding layer of pulse transformers are also true of ignition coils. By the term ignition coils, I am referring to ignition induction coils and ignition transformers, the only structural difference between which is a presence or absence of an air gap in the magnetic core. Ignition coils usually have added insulation between the last winding layer or two of the secondary winding and also fewer turns to provide spacing in the last winding layer to prevent inter-layer and inter-turn insulation breakdown due to the transient effects, of sparking across the spark plugs. The spaced turns and the added insulation are not required if the concepts mentioned above with respect to transformers are applied to ignition coils.

In FIG. 6, I have illustrated a partial cross-sectional view of the upper half of an ignition coil embodiment of my-invention, which comprises a core 71 of magnetic material that may be in the shape of a bar as illustrated, or that may form a closed loop or some other configuration. Insulators 73 and 77 insulate primary winding 75 of the coil from core 71 and from an electrostatic shield 7.9, respectively, which is also insulated by an insulation pad 81 from a first secondary winding layer 83. Layer 83, the start or low voltage turn of which is connected by a lead 85 to shield 79 and to an output terminal 87, is separated from the next winding layer 89 by an insulation pad provided in two sections 91. and 93 so that a lead 95 from the high voltage turnof layer 83 can pass between the sections to the low voltage turn of layer 89. For convenience of manufacture and compactness, lead'95 preferably follows a spiral path. But

as regards functionality, it could as well follow a straight line path or it could be placed outside the winding layers. The secondary winding layers following layer 89 are identical to layers 83 and 89and thus, except for the last layer 97, are not illustrated. They have the' same number of turns and width of traverse and the start of "each layer (low voltage end) is on the same side ofthe coil. Also, the highfvoltage end of each-layer is connected to the low voltage end of the next layer so that a uniform voltage distribution is obtained similar to that illustrated in FIG. for one of the Winding sets 17 or 19. "Thehigh voltage turn or 'end of the last layer 97 i connected by a lead 99' to an electrostatic shield 1 surrounding the coil, and also to an output terminal 103.

The shields 79 and 101 are not tapered because although tapering provides optimum operation, the insulation between the shields and the adjacent winding layers is so thin that it would be more difiicult to arrange the insulation like the insulation 55 in FIG. 1 than the improved results would justify. Also, since-there are many more layers in an ignition coil than in a pulse transformer, the capacitance between the shields and adjacent winding layers is not so important as in a'pulse transformer where this capacitance is a large portion of the total distributed capacitance of the transformer. Conceivably, shield 79 could be eliminated and core 71 used for the inner shield. But then the primary winding layer 75 would be between shields which is undesirable because it has a different voltage distribution than the secondary winding layers and thus would adversely aifect the substantially uniform voltage distribution. However, if the primary winding layer 75 is made the last layer in the coil instead of the first, as is sometimes done, that is if it is wound about shield 101, then core 71 could be used for the inner shield.

Due to the uniform electrostatic energy distribution in the coil and the presence of shield 79 and 101, practically all of the electrostatic energy stored in the secondary winding layers is discharged directly through the shields without passing along the winding layers. Therefore, the last layer 97 can be insulated and wound just like the other secondary winding layers, for the transient voltages will be so low in magnitude due to the direct discharge of the distributed capacitance energy that they will not be sufiicient to rupture the insulation. Also, as is disclosed in my copending application, Serial No. 732,348, Patent No. 2,995,685, the rapid substantially total discharge of the distributed capacitance makes the distributed capacitance energy available for firing of the spark plugs and thus increases the efiiciency of the ignition system.

While the invention has been described with respect to certain specific embodiments, it will be appreciated that many modifications and changes may be made by those skilled in the art without departing from the spirit of the invention. I intend, therefore, by the appended claims, to cover all such modifications and changes as fall within the true spirit and scope of my invention.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. An ignition coil comprising a magnetic core, a primary winding adapted to have a voltage applied thereto wound about said core, a first electrostatic shield around said primary winding, a plurality of similar capacitively interrelated secondary winding layers inductively related to said primary Winding with corresponding voltage points juxtaposed wound around said first electrostatic shield, a second electrostatic shield around said secondary winding layers, a lead for connecting the low voltage turn of said secondary winding layers to said first electrostatic shield, a lead for connecting the high voltage turn of said secondary winding layers to said second electrostatic shield and means sequentially interconnecting said secondary winding layers in the same sequential order as their winding order about said core.

, 2. An ignition coil comprising a magnetic core, a primary winding adjacent said core and adapted to have a voltage applied thereacross, a first electrostatic shield around said primary winding, a plurality of similar capactively interrelated secondary winding layers wound around said first electrostatic shield and which are inductively related to said primary winding, wherein all of said secondary windings have the same number of turns and wherein the low voltage ends of all of the secondary winding layers are at the same end of the coil, leads for connecting the high voltage end of each secondary winding layer to the low voltage end of the secondary Winding layer next furthest from said core, a second electrostatic shield around said secondary winding layers, a lead for connecting the low voltage turn of said secondary winding layers to said first electrostatic shield, and a lead for connecting the high voltage turn of said secondary winding layers-of a primary winding adapted to-have a voltage applied thereacross and two secondary windings inductively related to the primary wound longitudinally on said legs such that the high voltage ends of all the winding layers of each winding set are at the same end of the respective winding set, and leads inter-connecting winding layers of said winding sets such that from the second winding layer of each winding set to the last the voltages at the high voltage ends of all the winding layers for each Winding set increases in magnitude in accordance with the distance the respective winding layers are from the respective core legs, said winding layers from second to last being substantially identical and juxtaposed to provide the same voltage ditference between similarly related turns of adjacent layers.

4. The transformer as defined in claim 3 and two tapered electrostatic shields each one surrounding a different winding set and tapered such that the spacing between the low voltage end of the outermost Winding layer of each set and the respective shield is approximately equal to the spacing between winding layers while the spacing between the high voltage end of the outermost winding layer of each set and the shield is approximately zero, and leads for connecting the high voltage end turn of each of the outermost winding layer of each winding set to their respective electrostatic shield.

5. A transformer comprising a magnetic core having a plurality of core legs, first and second winding sets mounted on diiferent legs of said core and each including a single primary winding layer adapted to have a voltage. applied thereacross and a plurality of capacitively interrelated substantially identical winding layers from first and second secondary windings, wherein said winding layers are inductively related to said primary and wound longitudinally on said legs and arranged such that: each of said winding layers are juxtaposed and contains the same number of winding turns, the first winding layer of said first winding set is from the first secondary winding and of said second winding set is from the second secondary winding, the second winding layer of both of said winding sets is from the primary winding, the

-winding layers of both of said winding sets from the third winding layer to the last are alternately taken from the two secondary windings commencing with thesecond secondary winding for the first winding set and the first secondary winding for the second winding set, the outermost winding layers for the winding sets are from different secondary winding, and the winding layers are wound such that the high voltage ends of the windinglayers of any one winding set are at the same end of the winding set, said secondary winding layers being juxtaposed to provide a uniform voltage diiference between corresponding turns of adjacent layers.

6. The transformer as defined in claim 5 and two tapered electrostatic shields each around a difierent winding set and tapered such that the spacing between the low voltage end of the outermost winding layer of each set and the respective shield is approximately equal to the spacing between winding layers and the. spacing between the high voltage end of the outermost windinglayers of each set and the respective shields is approximately zero, and leads for connecting the high voltage ends of the outermost winding layers of the winding sets to the respective electrostatic shields,

7. A transformer comprising a magnetic core having a plurality of core legs, first and second winding sets mounted on different legs of said core and each including a winding layer from a primary winding adapted to,

receive a voltage and a plurality of capacitively interre-' ternately from the two secondary windings, the winding layers being wound such that the high voltage ends for the winding layers for any One set are at the same end of the set, leads interconnecting the winding layers of said sets such that the voltages at the high voltage. ends of each secondary winding layer increases in magnitude with the spacing of the respective winding layer from the respective core legs, said secondary winding layers beingequal and juxtaposed with corresponding turn-s spaced from one another so that a uniform voltage dilf'erence exists between corresponding turns of adjacent layers when said transformer is energized.

'8. The transformer as defined in claim '7 and two-tapered electrostatic shields, each around a diiferent windiug set and tapered such that the spacing between the low voltage end of the outermost winding layer of each set and the respective shield is approximately equal to the spacing between winding layers and the spacing between the high voltage end of the outermost winding layer of each set and the respective shield is approximately zero, and leads for-connecting-the high voltage ends of the outermost winding layers of the winding sets to the respective electrostatic shields.

9. A coil comprising a magnetic core, a primary wind- 1 ing layer adapted to have a voltage applied there-across and secondary winding layers inductively related to said primary winding wound longitudinally about said core,

said secondary winding layers comprising a plurality of a winding layer, coupling means for applying a voltage to said primary winding layer, similar secondary winding layers inductively related to said primary winding woundlongitudinally about said core whereby said layers arecapacitively interrelated, all said secondary winding layers being wound to have adjacent high voltage ends, and

means interconnecting the high voltage end of each sec ondary winding layer except the outermost secondary winding layer to the low voltage end of a secondary winding layer next further from said core whereby the. voltages at said high voltage ends progressivelyincrease in a direction away from said core, said secondary windinglayers being juxtaposed so there is a uniform; voltage gra dient between corresponding portions of adjacent layers.

11. A coilcomprising a magnetic core, a primary winding wound thereon adapted 'to have a voltage applied thereacros-s, substantially similar secondary winding lay: ers wound along said core inductively related to the pri and'juxtaposed with respect to one another to estab-v lish a common differential of voltage along all said wind.- ing layers with respect to one another and a common differential of voltage between layers when said primary is energized, means serially connecting said secondary winding layers in additive polarity relation so that the voltages in the secondary winding layers progressively change in the same sense radially out from the core, and

12. A coil comprising a magnetic core, a primary winding layer adapted to have a voltage applied thereacross and secondary winding layers inductively related to said primary winding and wound longitudinally about said core, said secondary winding layers comprising a plurality of equaladjaCent capacitively interrelated'winding layers all juxtaposed such that corresponding turns of said adjacent winding layers are adjacent, means serially connecting secondary winding layers in an additive polarity sense with each winding connected to the next in an outwardly progressing sequence such that when the primary is energized the voltages in the secondary layers progressively increase radially out from the core to provide a uniform voltage gradient throughout, and a shield connected to the high voltage end of the outside winding layer which at least partially surrounds said winding layers and which is tapered with a decreasing diameter toward the high Voltage end of the outside winding layer.

13. A transformer comprising a magnetic core having a plurality of core legs, plural winding sets mounted on different legs of said core and each including a winding layer from a primary winding adapted to have a voltage applied thereacross and a plurality of capacitively interrelated Winding layers from plural secondary windings wound longitudinally on said legs, wherein the secondary winding layers on each leg are equal, inductively related tothe primary Winding on that leg, and alternately from different secondary windings, the winding layers being wound so that when the transformer is energized the high voltage ends for the Winding layers in a set are at the same end of the set, leads interconnecting the Winding layers providing a secondary winding progressively composed of winding layers in a consistent polarity sense from first one set and then from another with successively higher voltage winding layers being placed over next lower voltage winding layers from another secondary to maintain a uniform voltage distribution between all layers.

14. A transformer as set forth in claim 13 having tapered shields at least partially enclosing the winding layers on each of said legs, and means coupling each of said shields to the high voltage end of the outermost winding layer on the corresponding leg, said shi-eldsdecreasing in diameter towards the high voltage ends of the corresponding winding layers.

15. A transformer as set forth in claim 13 wherein Said winding legs are substantially parallel to one another and wherein two winding sets are wound in opposite directions with the high voltage end of one winding set opposite the low voltage end of the other set so that the said interconnecting leads completing each of twosecondary windings are placed between adjoining ends of the winding sets, whereby a complete secondary winding proceeds in a spiral fashion comprising a winding layer running in one direction on one leg and then a winding layer running in the opposite direction on the other leg with higher voltage winding layers successively superimposed over next lower voltage Winding layers.

16. A coil comprising a magnetic core, a primary winding wound thereon, coupling means for applying a voltage to said primary winding, a plurality of superimposed secondary winding layers insulated from one another also wound on said core, said secondary winding layers being wound in a common direction and having substantially the same transformation ratio with respect to the primary winding wherein corresponding turns of said secondary winding layers are generally juxtaposed so that similar voltage points will be relatively aligned, voltage additive coupling means interconnecting a first end of a secondary winding layer with the correspondingly opposite end of a winding layer superimposed thereover to form a secondary winding wherein the same voltage differential exists between aligned turns of said superimposed layers, and a shield at least partially surrounding the secondary winding and connected to a first end of an outer winding layer.

References Cited in the file of this patent UNITED STATES PATENTS 1,932,640 Rust Oct. 31, 1933 1,940,840 Bellaschi Dec. 26, 1933 2,462,651 Lord Feb. 22, 1949 2,686,905 Schneider Aug. 17, 1954 2,862,195 Kury Nov. 25, 1958 

9. A COIL COMPRISING A MAGNETIC CORE, A PRIMARY WINDING LAYER ADAPTED TO HAVE A VOLTAGE APPLIED THEREACROSS AND SECONDARY WINDING LAYERS INDUCTIVELY RELATED TO SAID PRIMARY WINDING WOUND LONGITUDINALLY ABOUT SAID CORE, SAID SECONDARY WINDING LAYERS COMPRISING A PLURALITY OF SIMILAR ADJACENT CAPACITIVELY INTERRELATED WINDING LAYERS WOUND SUCH THAT THE HIGH VOLTAGE END OF EACH OF SAID ADJACENT WINDING LAYERS ARE ADJACENT, SAID LAYERS BEING POSITIONED SUCH THAT THE VOLTAGES AT SAID HIGH VOLTAGE ENDS PROGRESSIVELY INCREASE IN ONE DIRECTION ALONG SAID HIGH VOLTAGE ENDS, SAID SECONDARY WINDING LAYERS BEING JUXTAPOSED SO THERE IS A UNIFORM VOLTAGE GRADIENT BETWEEN CORRESPONDING PORTIONS OF ADJACENT LAYERS. 